AppVeyor: attempt to install .Net Core SDK 2.1.105 manually

appveyor.yml

@@ -1,6 +1,18 @@
 image: Visual Studio 2017
+init:
+   - git config --global core.autocrlf true
+install:
+   # Download .NET Core SDK 2.1.105 and add to PATH
+   - ps: $urlCurrent = "https://dotnetcli.azureedge.net/dotnet/Sdk/2.1.105/dotnet-sdk-2.1.105-win-x64.zip"
+   - ps: $env:DOTNET_INSTALL_DIR = "$pwd\.dotnetsdk"
+   - ps: mkdir $env:DOTNET_INSTALL_DIR -Force | Out-Null
+   - ps: $tempFileCurrent = [System.IO.Path]::GetTempFileName()
+   - ps: (New-Object System.Net.WebClient).DownloadFile($urlCurrent, $tempFileCurrent)
+   - ps: Add-Type -AssemblyName System.IO.Compression.FileSystem; [System.IO.Compression.ZipFile]::ExtractToDirectory($tempFileCurrent, $env:DOTNET_INSTALL_DIR)
+   - ps: $env:Path = "$env:DOTNET_INSTALL_DIR;$env:Path"
 build_script:
-  - build.cmd Test quick
+   - build.cmd Test quick
 test: off
 deploy: off
 shallow_clone: true
+clone_depth: 1